Anionics with weak

By analogy with the kinetic protonation of steroidal zl -enolate anions with weak acids such as acetic acid, which proceeds at the C-4 atom, since the maximum negative charge resides at this position (54,55), the kinetic protonation of the -dienamines with weak acids also occurs at this... 

Anionics with weakly basic cationics or amphoterics... 

BEC titration. Most mixtures of anionics with weakly basic cationics or amphoterics can be analysed by BEC titration in acid and alkaline solution. Two-phase titration is more satisfactory than potentiometric. Acid and alkaline have the same meanings as before. The measurements produced are shown in Table 8.3. 

Table 8.3 Titration of mixtures of anionics with weakly basic cationics or amphoterics...

So far we have considered the formation of radical anions only under very strongly reducing conditions, the electrons being provided by alkali metals, by solutions of alkali metals in liquid ammonia, or by less stable radical anions. This, however, is not at all essential. All that is needed is an anion with weakly bound electrons to act as a reducing agent. A very nice example of such a process is provided by the replacement of the exocyclic group in (60) by thiophenol. 

Many attempts have been made to find alternatives to the most reactive onium salt photo initiators bearing the AsFe" and SbFg" anions. These efforts have mainly been in response to the perception of toxicity and/or the possibility heavy metal contamination due to arsenic- and antimony-containing residues that are of concern in certain applications. In recent years, there has been considerable progress in the development of novel anions with weakly coordinating (i.e., low nucleophilic) character. For example, Castellanos et al7 have introduced diaryliodonium salt photoinitiators with the tetrakis(pentafluor-ophenyl)borate ((C6F5)4B ) anion. Following closely on this... 

The first successful hydrogenation reactions in ionic liquids were studied by the groups of de Souza [45] and Chauvin [46] in 1995. De Souza et al. investigated the Rh-catalyzed hydrogenation of cyclohexene in l-n-butyl-3-methylimidazolium ([BMIM]) tetrafluoroborate. Chauvin et al. dissolved the cationic Osborn complex [Rh(nbd)(PPh3)2][PFg] (nbd = norbornadiene) in ionic liquids with weakly coordinating anions (e.g., [PFg] , [BFJ , and [SbF ] ) and used the obtained ionic catalyst solutions for the biphasic hydrogenation of 1-pentene as seen in Scheme 5.2-7. 

Rh(nbd) (PPh3)2][PFg] (nbd = norbornadiene) in ionic liquids with weakly coordinating anions. 

An example of a biphasic, Ni-catalyzed co-dimerization in ionic liquids with weakly coordinating anions has been described by the author s group in collaboration with Leitner et al. [12]. The hydrovinylation of styrene in the biphasic ionic liq-uid/compressed CO2 system with a chiral Ni-catalyst was investigated. Since it was found that this reaction benefits particularly from this unusual biphasic solvent system, more details about this specific application are given in Section 5.4. 

The fact that ionic liquids with weakly coordinating anions can combine, in a unique manner, relatively high polarity with low nucleophilicity allows biphasic catalysis with highly electrophilic, cationic Ni-complexes to be carried out for the first time [26]. 

It will be recalled that in Chapter 7, in dealing with the anions of weak acids, we found that we were able to obtain good qualitative agreement between theory and experiment, if we replaced Jmv by the electrostatic Jti. As has been pointed out more than once, the use of simple electrostatic theory necessarily implies that there is an increment in the degree of order in the solvent subject to the electrostatic field. In the -coefficients of Table 24, however, we have found that for 6 out of the... 

Weakly acidic cation exchangers (e.g. polymethylacrylic acid resins). These resins (Zerolit 226, Amberlite 50, etc.) are usually supplied in the hydrogen form. They are readily changed into the sodium form by treatment with 1M sodium hydroxide an increase in volume of 80-100 per cent may be expected. The swelling is reversible and does not appear to cause any damage to the bead structure. Below a pH of about 3.5, the hydrogen form exists almost entirely in the little ionised carboxylic acid form. Exchange with metal ions will occur in solution only when these are associated in solution with anions of weak acids, i.e. pH values above about 4. 

TITRATION OF ANIONS OF WEAK ACIDS WITH STRONG ACIDS DISPLACEMENT TITRATIONS 10.17... 

J.ll In each of the following salts, either the cation or the anion is a weak acid or a weak base. Write the chemical equation for the proton transfer reaction of this cation or anion with water (a) NaC6H50 (b) KCIO (c) C,HSNHCI ... 

J.I3 Na As04 is a salt of a weak base that can accept more than one proton, (a) Write the chemical equations for the sequential proton transfer reactions of the anion with water. Identify the acid and the base in each reaction, (b) If 35.0 g of Na3As04 is dissolved in water to make 250.0 ml. of solution, how many moles of sodium cations are in the solution ... 

At last, barium and calcium complexes of phosphonium bifluorenylide 19 was obtained from the corresponding phosphonium iodide (Scheme 12). The anion displays weak nucleophilicity toward both cations which prefer to coordinate with neutral oxygen of THF and with iodide. Located outside the coordination sphere of the metals, it represents thus the first example of uncomplexed phosphonium diylide [59]. 

Thioethers lack the capacity to neutralize positive charge and display weak donor properties. Consequently, they do not readily displace strong donor solvents (water) or strongly bonding anions (such as halides) from the coordination sphere. As a consequence, many thioether complex syntheses employ aprotic or alcoholic solvents and precursor complexes with weakly bound solvents (such as DMSO or acetone) or anions (such as C+3S03 ). Despite the synthetic challenges, a wide range of complexes has been reported, particularly with the cyclic poly-thioethers, where the macrocyclic effect overcomes many of the above difficulties. 

The plot of permeability coefficient versus molecular radius in Figure 10 shows the interdependence of molecular size and electric charge. The permeability of the solutes decreases with increasing size. The protonated amines permeate the pores faster than neutral solutes of comparable size, and the anions of weak acids permeate the pores at a slower rate. The transport behavior of the ionic permeants is consistent with a net negatively charged paracellular route. These results are phenomenologically identical to those found in the transport kinetics of... 

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